This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Most of the activity of environmentally ubiquitous polycyclic aromatic hydrocarbons (PAH) and related dioxin are mediated by the AhR (aryl hydrocarbon receptor). The AhR is a member of the Per/ARNT/Sim (PAS) family of transcription factors and is known to be associated with neurological development, circadian cycle and angiogenesis. The AhR contains a DNA binding and protein dimerization site in its N-terminal bHLH domain, a ligand binding site in the PAS homology domain, nuclear localization and export sequences, and a transcriptionally active Q-rich domain. Upon ligand binding, the receptor translocates into the nucleus and associates with at least one co-factor, ARNT. The activated AhR complex then binds promoter regions of a number of target genes at specific DNA-binding sites, resulting in gene transcription. If the AhR is constitutively active in tumor cells and its transcriptional activity affects functions which are critical to those cells, then it wou ld b e expected that the composition of the active AhR complex would be different in tumor cells than in their non-transformed counterparts. The purpose of this study is to identify and compare the AhR-associated proteins in transformed human fetal kidney cell lines in which AhR is constitutively active to those present in normal cells. Initial MALDI-TOF MS data analysis for samples derived from the GST-AhR transfected 293T cell line showed a number of protein bands (120 kDa, 90 kDa, 42 kDa and 35 kDa) and data base searches identified some of the proteins (HSP, BMALI), which are known to be associated with the AhR complex. We are in the process of sequencing additional peptides by MS/MS.